This invention relates to a method of cleaning a plasma processing device of the type having a remote plasma source for generating radicals which are used to perform the cleaning. The invention relates also to associated plasma processing devices.
In the manufacture of semiconductor products, PECVD (plasma enhanced chemical vapour deposition) deposition of dielectric materials is required for isolation and passivation purposes. These processes can be used in applications which range from front-end device to back-end Through Silicon Via (TSV), via reveal and interposer manufacture. Regular cleaning of the PECVD process chamber is required between wafer processing operations to prevent the creation and accumulation of contaminant particles. These contaminant particles affect the performance and reliability of the deposited dielectric films, resulting in low wafer yield and premature device failure. Two techniques are commonly used for cleaning. These techniques are direct plasma cleaning and remote plasma source (RPS) cleaning.
Direct plasma cleaning involves the creation of a plasma in the process chamber itself for cleaning purposes. Direct plasma cleaning of silicon based dielectric films such as silicon dioxide and silicon nitride typically involves the detection of an optical end-point signal to determine when to stop the cleaning process. This is achieved by monitoring plasma intensity in the chamber by detecting suitable emissions, such as emission from ionised fluorine. U.S. Pat. No. 7,354,778 discloses end-point detection in a direct plasma cleaning process in which a DC bias voltage of the plasma generator is monitored. Because the plasma generator is part of the direct plasma cleaning arrangement, the cleaning is performed using ionised process gases created in the chamber itself. Accordingly, the concentration of charged particles which would be expected to give rise to the DC bias voltage in the chamber is relatively high.
An RPS cleaning system does not produce plasma inside the PECVD chamber, and so it is not possible to detect an optical end-point signal in the chamber, as there is no plasma in the chamber to produce an optical output. Additionally, there is no direct source of charged particles within the PECVD process chamber, which will be anticipated to dramatically reduce the concentration of charged particles available to produce a DC bias signal of the type detected in U.S. Pat. No. 7,354,778.
In contrast, an advantage associated with many RPS cleaning methodologies is that cleaning is performed primarily using radical species. The decoupling of the remote plasma source from the PECVD chamber in which cleaning takes place results in the majority of the charged species created by the cleaning plasma being prevented from entering the PECVD chamber. The consequent reduction of ion bombardment in the PECVD chamber has the advantage of resulting in less wear on chamber components. This has the consequential advantage of reducing the frequency of chamber interventions for maintenance purposes.
U.S. Pat. Nos. 6,079,426, 6,543,459, and US2006/0090773 describe the detection of cleaning end-points for RPS devices. U.S. Pat. No. 6,079,426 and US2006/0090773 disclose the detection of a cleaning end-point by monitoring chamber pressure. U.S. Pat. No. 6,543,459 discloses a method of determining a cleaning end-point for a remote microwave plasma cleaning system in which capacitance changes are monitored. Another end-point detection technique uses infrared detection of a cleaning end-point. The measurements are made in the vacuum exhaust line downstream of the process chamber. This technique has been commercialised as the Process Sense® end-point sensor by MKS Instruments, Inc. of Methuen, Mass. 01844, USA.